Extreme technique · Technique Academy

XY-Chain

An XY-Chain is a run of two-candidate cells in which each neighbour shares a digit with the next, the chain starting and ending on the same digit. It is an XY-Wing that did not know when to stop.

Professor Cryptic, the owl who teaches in the app
Professor Cryptic is thinking

The reasoning

Why does the XY-Chain work?

Passing the baton from cell to cell, one of the two end cells must hold that shared digit. So any cell that sees both ends can lose it.

A worked example

What does the XY-Chain look like on a real board?

XY-Chain worked exampleA sudoku board with pencil marks. The XY-Chain uses R1C4, R1C9, R6C9, R5C7, R5C6 and digit 2 (5 cells). The move strikes candidate 2 in R4C4.8152927624734942796183275293279272494758166247272491385583762424911249538672493182424567258617943764359128
The move strikes candidate 2 in R4C4. Digit 2, 5 cells.
  • Cells that form the pattern
  • Cells that lose a candidate
  • Struck digit: ruled out

Make it stick

How can you practise the XY-Chain?

The Technique Academy in Cryptic gives every technique its own lesson and 5 practice boards that need exactly this move.

Get it onGoogle PlayPlay Cryptic on the web

Further reading: HoDoKu's page on this family of techniques.

EasierSimple ColoringHarderX-Chain